Technical Standards and Safety Authority (TSSA) G3 Practice Exam

Which of the following is an indication of incomplete combustion?

1. High levels of CO2

2. Completely clear flame

3. Visible soot or smoke

4. Low heat output

The correct answer is: Visible soot or smoke

The presence of visible soot or smoke is a clear indication of incomplete combustion. In a combustion process, complete combustion occurs when the fuel burns entirely, producing carbon dioxide and water as the main products, with minimal to no other byproducts. When combustion is incomplete, the fuel does not burn efficiently, leading to the formation of carbon particles, which appear as soot, and other unburned hydrocarbons that create smoke. This not only indicates a problem with the combustion process but also can be a sign of insufficient oxygen supply, incorrect fuel-to-air ratio, or malfunctioning equipment. In contrast, high levels of carbon dioxide indicate that combustion is occurring, though they don’t reflect its completeness. A clear flame typically suggests complete combustion, as it indicates that the fuel is burning efficiently and cleanly, thereby producing minimal soot. Lastly, low heat output can occur in both complete and incomplete combustion scenarios and does not specifically indicate that incomplete combustion is taking place. Therefore, visible soot or smoke is a direct and recognizable indicator of incomplete combustion.